An experimental study: does the neuroprotective effect increase when hypothermia deepens after traumatic brain injury?

Background: Experimental approaches have been promising with the use of therapeutic hypothermia after Traumatic Brain Injury (TBI) whereas clinical data have not supported its efficacy.

Objectives: This study aimed to investigate whether using selective deeper brain cooling correlates with a more neuroprotective effect on Intracranial Pressure (ICP) increments following TBI in rats.

Materials And Methods: Adult male Sprague-Dawley rats (mean weight = 300 g; n = 25) were subjected to brain injury using a modified Marmarou method. Immediately after the onset of TBI, rats were randomized into three groups. Selective brain cooling was applied around the head using ice packages. Intracranial Temperature (ICT) and ICP were continuously measured at 0, 30, 60, 120, and 180 minutes and recorded for all groups. Group 1 (n = 5) was normothermia and was assigned as the control group. Group 2 (n = 10) received moderate hypothermia with a target ICT of between 32°C - 33°C and Group 3 (n = 10) was given a deeper hypothermia with a target ICT of below 32°C.

Results: All subjects reached the target ICT by the 30th minute of hypothermia induction. The ICT was significantly different in Group 2 compared to Group 1 only at the 120th minute (P = 0.017), while ICP was significantly lower starting from the 30th minute (P = 0.015). The ICT was significantly lower in Group 3 compared to Groups 1 and 2 starting from the 30th minute (P = 0.001 and P = 0.003, respectively). The ICP was significantly lower in Group 3 compared to Group 1 starting from 30th minute (P = 0.001); however, a significant difference in ICP between Group 3 and Group 2 was observed only at the 180th minute (P = 0.047).

Conclusions: Results of this study indicate that selective brain cooling is an effective method of decreasing ICP in rats; however, the deeper hypothermia caused a greater decrease in ICP three hours after hypothermia induction.